1. Field of the Invention
The present invention relates to solder connections between aluminum and copper conductors.
2. Description of the Prior Art
Aluminum, while being a good conductor, is a relatively reactive metal and has a tendency to form a layer of aluminum oxide coating on the surface thereof by reacting with the air. This aluminum oxide coating prevents the soldering of the aluminum wire to a copper conductor with conventional lead-tin solder and rosin or mildly activated rosin fluxes, for example, type RMA, U.S. Federal Specification QQ-S-571. As a result the prior art removes the aluminum oxide from the aluminum utilizing highly aggressive fluxes including very active corrosive flux of fluoride components. The use of such agressive fluxes, however, is undesirable in sophisticated electronic equipment wherein sensitive components when subjected to such fluxes would tend to corrode and fail prematurely.
An alternate way of joing the aluminum conductor is by preliminarily electrochemically plating a layer of copper or other metal having a less refractory oxide onto the aluminum surface by electrical, chemical, or other means. For example, after removal of the aluminum oxide skin from aluminum wire or conductor and without exposure to air, a layer of copper, silver or copper alloy can be deposited upon the clean exposed aluminum. This plating protects the aluminum from further oxidation and yet forms a basis for joining with another dissimilar metal for example a copper conductor. This process, however, is quite cumbersome and costly. It is not readily adaptable to production techniques on a commercial basis. The reason is that each wire would have to be completely coated with the copper coating after being severed to its useful configuration. Since hundreds, and possibly thousands of individual conductors may form a single wiring harness configuration, the individual plating of each wire can be a relatively difficult and time-consuming task.